1. Field of the Invention
This invention relates to a buzzer damping sound producing device, and more particularly to a buzzer damping sound producing device in which a fundamental frequency pulse signal is applied to a buzzer to repeatedly produce a damping sound with a predetermined period.
2. Background
A conventional buzzer damping sound producing device of this type is shown in FIG. 8.
In FIG. 8, reference numeral 1 designates a control circuit comprising a micro-computer (CPU) which operates according to a predetermined program. The control circuit 1 has a terminal OP.sub.1 through which a pulse signal having a period T (having a first waveform) is outputted, and a terminal OP.sub.2 through which a pulse signal of a fundamental frequency (having a second waveform) is outputted.
Reference numeral 2 designates a two-stage amplifier circuit including amplifying transistors Q.sub.1 and Q.sub.2. A capacitor 3, receiving the first waveform amplified by the amplifier circuit 2, is repeatedly charged and discharged to thereby form a damping voltage signal (having a third waveform). The second waveform is amplified by a one-stage amplifier circuit including an amplifying transistor Q.sub.3. An output circuit 5 includes a transistor Q.sub.4 which receives the second and third waveforms and outputs to a buzzer 6 a buzzer operating damping signal (having a fourth waveform), which is modified with the second and third waveforms 6. In the conventional circuit, the buzzer is typically driven with a signal of 5 volts.
In more detail, the pulse signal having the first waveform is provided at the output terminal OP.sub.1 of the control circuit 1. This pulse signal is applied to the capacitor 3, so that the capacitor is repeatedly charged and discharged with the period T, thus outputting the signal having the third waveform. The signal thus outputted is applied to the output circuit 5, to which the pulse signal of the fundamental frequency (having the second waveform) is applied through the terminal OP.sub.2 of the control circuit 1. As a result, the pulse signal of the fundamental frequency (the second waveform) is modulated with the above-described signal having the third waveform, so that the signal having the fourth waveform is formed. The signal thus formed is applied to the buzzer 6, so that a buzzer damping sound waveform, as shown in FIG. 9 is obtained.
In the conventional buzzer damping sound producing device thus designed, it is essential to use two kinds of pulse signals having different periods, and it is also necessary to perform an analog signal conversion by charging and discharging the capacitor 3. Hence, the conventional device is disadvantageous in that it is intricate in construction and requires a large number of components. Accordingly, it is difficult to reduce the size and weight of the modules thereof. Furthermore, the devices does not function adequately because the damping sound produced thereby is fundamentally of the same period.